Method and apparatus for vapour phase soldering

ABSTRACT

The present invention concerns a method and an apparatus for performing soldering of items that are applied a soldering agent, where the soldering apparatus includes at least one soldering zone, where the soldering zone include means for generating vapour, the apparatus being adapted to heat the items to be soldered to a temperature required for soldering by condensing the vapour. Further the invention relates to a method and an apparatus for flux deposition connected to a soldering machine, which soldering machine comprises a solder heating medium evaporated by heating means forming a vapour that heats elements to be soldered by heat transfer and by condensation, which apparatus comprises means for condensation, of a vapour containing flux where pumping means circulate vapor containing flux through the condensation means, where the condensation means comprises heat exchangers for cooling the vapour for flux condensation.

The present invention relates to a method and an apparatus forperforming soldering of items that are applied a soldering agent, wherethe soldering apparatus includes at least one soldering zone, where thesoldering zone includes means for generating vapour, the apparatus beingadapted to heat the items to be soldered to a temperature required forsoldering by condensing the vapour, and where the soldering zoneincludes gates.

The invention also relates to an apparatus for flux deposition connectedto a soldering machine, which soldering machine comprises a solderheating medium evaporated by heating means forming a vapour that heatselements to be soldered by heat transfer and by condensation, whichapparatus comprises means for condensation, of a vapour containing fluxwhere pumping means circulate vapour containing flux through thecondensation means, where the condensation means comprises heatexchangers for cooling the vapour for flux condensation.

The present invention also relates to a method for flux deposition inconjunction with vapour phase soldering, where a solder heating mediumis evaporated by heating forming a vapour, which vapour heats elementsto be soldered partly by condensation to a temperature above a solderingtemperature, which leads to soldering of elements, which solderingprocess leads to evaporation of flux and other chemical substances.

U.S. Pat. No. 5,181,648 discloses a vapour phase soldering apparatusstructured as several sections, where gates are provided at thetransition between the sections so that different closed compartmentsare provided in which the individual subprocesses occur. There is used acomplicated conveyor mechanism, as items to be soldered are submerged ina vapour phase over a vessel in which vapour is generated, why the itemsare to perform a vertical movement down into the vessel and to stay atthe bottom of the vessel until the conveying means in the form of aconveyor transports the items vertically upwards and further on througha flushing facility.

The relatively complicated conveying means, however, makes the disclosedmethod less applicable for mass production of large series of printboards, and there are limits to how large panels that can be soldered.

U.S. Pat. No. 4,838,476 also concerns a soldering apparatus of thevapour phase type, where soldering items are transported by acomplicated conveyor device, down into and up from a vessel containing aliquid in vapour phase. In order to avoid loss of heat as well as liquidthere are gates providing a phase division in the apparatus.

U.S. Pat. No. 4,580,716 describes a solder reflow process includingvaporized fluorinated organic liquid such as FC-70 is dehumidified bypressurizing the vapour chamber with dry nitrogen and blowing the drynitrogen against the conveyor belt and article to be soldered as theypass through the inlet throat. Inlet of nitrogen into the vapour chamberis pressing vapour through the coils and out in the inlet and outlet,from where vapour is lost.

DE-C2-196 15 337 discloses a method for making a vapour-free climaticzone above a vapour level in a vapour phase soldering apparatus. Inorder to ensure transparency in the upper part of the apparatus so thata camera can view the items during the soldering, a gas is injected forachieving partly condensation, where this gas either may be usual air oran inert gas. The blowing in of this gas will, however, be unfavourableand is to be controlled effectively in order not to put down the vapoursso much that soldering cannot be effected.

U.S. Pat. No. 6,382,500 describes a semiconductor soldering device. In asolder reflow furnace, flux is vaporized and carried to the furnaceexhaust pipe. The flux condenses on the walls of the exhaust pipe anddrips back into the furnace thereby contaminating production parts. Asolder reflow furnace with a flux effluent collector prevents fluxdrip-back. The flux effluent collector has an exhaust gas heater thatmaintains flux effluent in a gaseous state, a flux cooler, tosubsequently condense flux, and a flux condensation region where theflux condenses. The flux condensation region is offset from thefurnace's exhaust opening so that condensed flux cannot drip back intothe furnace.

U.S. Pat. No. 5,611,476 describes a solder reflow convection furnaceemploying flux collection and heating to minimize flux and solvent buildup and gas densification to reduce input gas flow. As solder melts inthe furnace, an effluent of vaporized flux is driven off and cancondense on cooler components. To minimize such condensation, the gas isdirected through a cooling system in which the flux condenses, and thecooled, purified gas is directed into the furnace's product coolingsection. In another embodiment, in which the gas in the furnace isrecirculated, a cooling coil is located upstream of the recirculatinggas mover to heat the primary gas. The vaporized flux condenses on thecooling coil, which can be readily removed and replaced. In anotheraspect of the invention, in which furnace employs a gas amplifier, therecirculating gas is cooled prior to reentry into the heating chamber,which increases its density and removes flux by condensation.

The above documents describe inventions by which it is possible toremove flux from a furnace in which a solder process takes place. Usedin combination with infrared reflow soldering, removing of flux takesplace in an efficient way. But used in vapour phase reflow solderingfurnaces, where a solder heating medium is evaporated by heating meansforming a vapour that heats and solder electronic boards by condensationof the vapour, the vapour is drawn out of the furnace. By contact to thecooling surfaces in the cooling system, the vapour is caused to condensetogether with the flux, thereby forming a mixture of liquid solderheating medium and liquid flux. It is important that separation ofliquid flux and liquid solder heating medium takes place in such a waythat solder heating medium is not lost.

It is the object of the invention to achieve a method and an apparatusfor condensation soldering of items, where the soldering may occur atminimal environmental load by minimising the loss of condensing vapourused for soldering. Also, it is an object of the invention to achievesolderings with high quality, where oxidation is reduced optimally whilethe soldering occurs. Another scope of this invention is to remove fluxfrom a vapour phase solder furnace without losing solder heating medium.

This may be achieved if the soldering zone contains a protective gas, ifthe soldering zone includes means for shutting off the vapour generatingmeans, and if the soldering zone is adapted for supplying means forforced condensing of condensing vapour at the end of a solderingprocess.

Hereby may be achieved that a soldering zone remains isolated from thesurroundings in the period of time in which vapour is generated so thatthis vapour will not have any possibility of evading out of thesoldering zone. The content of protective gas may simultaneously implythat the oxygen possibly contained in the soldering zone before vapourgeneration starts has been displaced long ago, whereby the oxygencontent, possibly by flushing with a protective gas, may be reducedconsiderably, and while this flushing occurs, the vapour generatingmeans may be shut off, after which opening the vapour generating meansprovides build up of a condensing vapour zone in the soldering zone ofthe soldering apparatus, whereby items to be soldered are heated by thecondensing vapour. Since the vapours have a temperature exceeding themelting point of a soldering agent, a temperature on the soldering itemsis made so high that soldering is started on the soldering items. Whenthe soldering process is expected to finish, i.e. when the solderingitem has had the desired temperature for a predetermined time, there isno longer use for the hot vapours, and the vapour generating means maybe shut off, after which a protective gas may be introduced in thesoldering zone, inducing forced condensing of vapours. When this forcedcondensing is advanced, a item to be soldered may be removedautomatically through a gate by a conveyor belt performing transport tothe succeeding zone. Thus there may be performed soldering where theheating gas remains in the soldering zone and where the items at a timewhen heated in proximity of the soldering temperature are exposed tocondensing vapours and protective atmosphere only. Thereby oxidation isreduced optimally.

Advantageously, a soldering process may take place by supplying aprotective gas to the soldering zone through ducts suited for thispurpose, where the supply of protective gas may occur in dependence ofmeasurement of the actual oxygen content in the soldering zone.

The soldering zone may contain means for pressure regulation, wheresuction facilities may remove an amount of gas from the soldering zonecorresponding to the supplied amount of protective gas. Hereby may beachieved that a substantial pressure increase in the soldering zone doesnot occur and simultaneously also that a substantial vacuum does notoccur either which possibly may suck further oxygen into the solderingzone through leakages. In order to reduce the content of oxygen in thesoldering zone and in the solder paste the pressure can be reducedbefore a protective gas is led to the soldering zone so that theprotective gas is drawn into the soldering zone, and afterwards vapouris drawn into the soldering zone, where the soldering process take placenear normal pressure.

The oxygen content in the soldering zone may be kept under apredetermined minimum value while the soldering occurs. Hereby may beachieved that injection of protective gas may be reduced and may bestopped completely in the period in which the soldering process occurs,but if the oxygen content in the course of the process is increased forsome reason, one will have the possibility of reducing the oxygencontent by additional supplying of protective gas.

At the end of a soldering process, protective gas at a temperature lowerthan the soldering temperature may be supplied to the soldering zone inorder to achieve forced condensing of vapours. Hereby may be achievedthat the condensing vapours are removed from the soldering zone in ashort time as the temperature in the entire soldering zone is reduced.This reduction of temperature is, however, to be effected inconsideration of the soldering item, which is not to be cooled abruptlyunder any circumstance as this may be detrimental for electroniccomponents, but even with a limited supply of temperate protective gas,rapid condensation of vapours will be obtained so that the solderingzone is rapidly freed from condensing vapour as the condensing vapour israpidly transformed into liquid, which is collected. An almost pureprotective, ambient atmosphere is thus attained around the items, afterwhich a conveyor belt may move the items into the next zone through asuitable gate which is opened and subsequently closed.

At the end of a soldering process, the soldering zone may be suppliedwith protective gas at a first high temperature, where the temperatureis approached a second lower temperature over a period of time. Herebymay be achieved controlled cooling of the items to be soldered. Thefirst temperature may be close to the soldering temperature.

By gradually lowering the temperature in the protective gas, condensingof the condensing vapour occurs gradually, and no abrupt cooling occurs.The entire cooling of items may effectively be controlled by regulatingthe temperature of the protective gas.

The soldering zone may contain a vessel heated by at least one heatingelement, where the vessel may be covered by means for shutting offincluding perforated plates that are mutually displaced by at least oneactuator. Hereby may be achieved that the vessel effectively may be shutoff by perforated plates so that vapours are prevented from rising upinto a process chamber. Under the closed plates vapours are released,which, as soon as the plates are moved to the open position, penetrateto the overlying soldering process chamber which is heated up. The useof reduced pressure in the process chamber is decreasing the time offorming a vapour phase in the process chamber, where a circulationinside the process chamber leads to a uniform heating.

The means for shutting off the vessel may advantageously be closed untilthe start of a soldering process where at least one heating element maybe activated at the start of the soldering process simultaneously withthe means for shutting off the vessel are opened. Hereby may be achievedthat the power supply in the vessel is increased at the moment the meansfor shutting off are opened. Thereby, the vapour formation may bereduced at times where no soldering is taking place and be increasedwhen the need for heating power is the greatest.

At the end of the soldering process, the means for shutting off thevessel may be closed simultaneously with the means for heating areswitched off. As previously mentioned, formation of vapours is herebyreduced at times when there is no need therefor.

Advantageously, the soldering apparatus may include a preheating zone,where soldering items may be preheated to a predetermined temperature,where the soldering apparatus may include at least one gate, and wherethe preheating zone includes at least a second gate at its entrance.Hereby may be achieved a gradual heating of items to be soldered whichis essential for electronic components, where ceramic capacitors inparticular cannot stand sudden changes in temperature. At the same time,the time items are to stay in the soldering zones is reduced so that thecapacity of the soldering apparatus is increased.

Advantageously, the soldering apparatus may include at least one coolingzone, where the apparatus includes at least on gate between solderingzone and cooling zone, where the cooling zone includes at least one gateat the exit. Hereby may be achieved that a cooling zone performs slowcooling of items in order to avoid stressing of possible electroniccomponents.

Advantageously, the soldering apparatus may contain means fordetermining the position of the items to be soldered, where the openingand closing function of the gates of the apparatus are determined fromthe position of the items and the actual conditions in the zones of thesoldering apparatus. Hereby may be achieved a conditioned opening of thegates of the soldering apparatus, where the conveyor systems of theapparatus may be adapted for only performing conveying to a positionmeasurement and to wait there, if, for different reasons, there is nopossibility of opening the next gate. Hereby may be constructed a veryflexible apparatus that may operate automatically, where items in theform of e.g. printed circuit boards may run through the apparatus in acontinuous flow, though interruptions in the operation may arise due todifferent causes, which are relieved automatically as the gates remainclosed and the conveyor belts are stopped.

With this apparatus, pumping means are stopped during the solderingprocess, and started upon ending a solder process. The pumping meansoperate in a closed circuit starting at an outlet from the solderingprocess and ending at an inlet to the soldering process. The closedcircuit may comprise at least a first heat exchanger operating at afirst temperature, and at least a second heat exchanger operating at asecond lower temperature, where the heat exchangers can be placed inconjunction with liquid collecting means. In this way it can be achievedthat the two condensation processes can take place in heat exchangerswhere the condensation does not necessarily take place with energylosses to the surroundings, because the energy delivered from the heatexchangers can be used in the soldering process for preheating ofprinted circuit boards before the boards enter the soldering zone. Thispreheating is necessary for avoiding temperature shocks during thesoldering process.

A protective gas may be mixed with the vapour during the solderingprocess. The presence of a protective gas reduces oxidation during thesoldering process. As is known, oxidation may occur not only on thesoldering material but also the in the evaporated flux. Oxidation isundesirable because it often leads to the formation of carbon particles.Likewise, the presence of protective gas prevents the components on theprinted circuit boards from being oxidized during the soldering process.The use of the protective gas could also lead to the use of a solderingpaste containing only a very limited amount of flux. In the future itshould also be possible to perform entirely flux-free soldering if thesoldering takes place in an environment with protective gas.

The closed circuit may also comprise at least one heat exchanger forheating protective gas to a temperature below the condensing temperatureof the vapour before the protective gas is returned to the solderingdevice in a time periods after soldering is finished. Preheating of theprotective gas is important in order to avoid temperature shocks onprinted circuit boards. Especially ceramic capacitors are very sensitiveto large temperature fluctuations, and cracks in the ceramics can changeto capacitors to resistors in a few hours. However, by heating theprotective gas to 150° C. for example, the temperature shock is reducedto less than 50° C. However, this temperature is sufficiently low forcondensation of the vapour of the solder heating medium. Thus by pumpingin preheated protective gas in a rather fast manner, the vapour isremoved in only a few seconds.

Liquefied solder heating medium can be returned from the liquidcollecting means through a conduit to a flux trap comprising steps,which flux trap is cooled by cooling means to a first condensationtemperature and further cooled to a second lower temperature for fluxliquefying. By using a flux trap made of a large number of small steps,the temperature can be reduced from step to step. The liquid solderheating medium passes the steps, and the temperature is graduallyreduced. In this way the content of liquid flux is solidified and byforming the steps at a negative angle, liquefied particles will becollected in the steps and can later be mechanically removed by cleaningof the equipment. Depending on the kind of flux used, the temperaturecan be reduced to a very low level, maybe as low as 20° C., but becauseof the necessary re-heating of the medium, the temperature will bereduced to exactly the temperature at which all the flux is liquefied,thereby saving energy.

The heat exchangers may comprise cooling fins that are tilted againstthe inlet direction in order to return liquefied solder heating mediumand liquefied or solidified flux, in which the protective gas can passover and around the fins. The tilted position of the fins is efficientfor collecting heavy flux particles whereby small drops of flux heat thefins by which the fins are further cooled, and liquid flux flowsdownwards on the fins opposite the flow direction. From the fins, theflux can fall down as droplets. The surface of the fins can be made insuch a way that there are no fixation points at all for liquid flux toadhere to so that the liquid flux will automatically start flowingbackwards by way of gravity as soon as droplets exceeding a certain sizeare formed. Thus the fins are self-cleaning.

Liquefied solder heating medium and liquefied or solidified flux canpass through filter means before reaching collecting means, which filtermeans can collect liquid or solidified flux and other chemicalsubstances. By letting all the liquids that leave the heat exchangerspass through filters, a large part of the flux will be collected inthese filters, and the filters can afterwards be cleaned and reused inthe soldering machine.

Liquid solder heating medium can be collected at the surface of a trayplaced under the soldering zone and led over the flux trap. Here by isachieved that also flux that has reached the boiling tray under thesoldering zone can be collected in the flux trap. Liquid solder heatingmedium is pumped to the flux trap in periods the flux trap has freecapacity, whish occur in periods between solder processes. After passingthe flux trap the solder heating medium is returned to the tray whereheating elements are heating the solder heating media for formingvapour.

Surfaces on elements in contact with flux might be coated with amaterial having ability not to fix liquid or solidified flux. In thisway flux is removed from the surfaces primarily by liquid solder mediumflowing back passing the liquid trap or the flux is ending in the trayunder the soldering zone, and from here the solder heating medium iscolleted and led over the flux trap.

The pressure in the soldering zone can be reduced at the beginning of asoldering process, where the pressure is partly normalised by opening avalve for supply of protective gas into the soldering zone, where thepressure in the soldering zone is normalized by opening for supply ofvapour. In this way at first oxygen is drawn out from the solderingzone. Afterwards the protective gas is added so the oxygen is partlyreplaced by the protective gas, which might be important for thereduction of oxidisation during the soldering process. If the pressureis reduced the vapour can very fast fill the volume of the solderingzone after opening the valve placed over the vapour generating means.After the soldering process the vapour is drawn out from the solderingzone through condensing means, from which the liquefied vapour is ledback through flux filtration means to vapour generating means.

The invention also concerns a method where the soldering process step iseffected in the presence of a protective gas, and that the second stepincludes shutting off the supply of vapour and forced condensing ofvapour. Hereby may be achieved solderings with good quality as oxidationmay be completely avoided, and since the condensing vapour may be putdown and since further supply of condensing vapours may be shut off,soldering largely without loss of condensing vapour may be achieved,where possible suction facilities in connection with the solderingapparatus may include special means for forced condensing of condensingvapour, whereby even small amounts of condensing vapours may berecovered, which might comprise the use of under pressure andrecirculation through condensing means.

Supply of protective gas may be used as means for forced condensing ofthe condensing vapours. Hereby may be achieved that the soldering zoneis filled with protective gas as soon as a soldering process has beenperformed, whereby a commencing drop in temperature results insolidifying of soldering agent, and a commencing cooling of the items.The condensing vapour is transformed into a liquid which is collected.Gates for preheating zone and cooling zone may be opened subsequentlywithout loss of the condensing vapour, and only the protective gas haspossibility of evading through the open gates.

This can be achieved by a method as described in the introduction, whichmethod is modified in such a way that vapour of solder heating mediumcontaining flux and other chemical substances is drawn into a closedcircuit in time periods between and after soldering processes, where theclosed circuit comprises at least a first condensation process and asecond condensation process, which first and second condensationprocesses take place at a first high and a second lower temperature, andliquid solder heating medium is returned to the vapour phase solderingprocess.

Hereby it can be achieved that after completion of a soldering processwhere, for example, a printed circuit board has been fully soldered, theflux, which was contained in the soldering paste placed on the board, toa large extent is evaporated and consequently mixed up with the solderheating medium. Thus after completion of the soldering process, amixture of flux and solder heating medium is sucked out of the solderingchamber and into a closed circuit in which purification of the solderheating medium takes place. This purification is done by removal of theflux content from the mixture by passing it through condensation means,where condensation at a first high temperature takes place by which mostof the flux contained in the mixture is condensed. In this firstcondensation process, the solder heating medium itself is also partlycondensed. The liquid substance resulting from the condensation processdrips down from the condensation means and into a collector part therebyconducting the rest of the solder heating medium, which still maycontain a small content of flux, to a second condensing means where thecondensation takes place at a lower temperature than in the firstcondensation process. It is ensured that almost all solder heatingmedium is condensed in that the temperature of the condensation processis lower than the boiling temperature of the solder heating medium. Theresult of this process is that that most of the flux that has evaporatedduring the soldering process is now collected inside a closed circuitand as such totally removed from the soldering process.

The first high condensation temperature depends on the condensationtemperature of the flux, whereas the second lower temperature depends onthe condensation temperature of the solder heating medium. If it ispossible to define the exact condensation temperature of the flux, itwill be possible to effect almost full condensation of flux at the firstcondensation temperature. If the difference between the condensationtemperature of the solder heating medium and the condensationtemperature of the flux is sufficiently high, it is possible to fullyseparate the two gases into different liquids. In practice, however, theflux has a very complex composition where the condensation can takeplace over a relatively large temperature range. Probably both flux andsolder heating medium will be condensed at the second (lower)condensation temperature.

The method may also comprise the use of a protective gas during thesoldering process, which protective gas is mixed with the vapour. Theuse of the protective gas is important during the soldering processbecause the protective gas prevents oxygen from getting into contactwith the melted solder. But also before melting of the solderingmaterial, the temperature is high. If solder paste is used, which mayhave a relatively large surface, oxidation may start already during thepreheating of the devices to be soldered. The protective gas will bemixed with the vapour of the solder heating medium during the wholeprocess. After completion of the soldering process, vapour continues tobe drawn out of the chamber, and the mixture of flux, vapour of thesolder heating medium and protective gas is led through the condensingunits. The condensing units will remove flux and solder heating mediumand leave almost purified protective gas.

The protective gas can be heated by heating means to a temperature belowthe condensation temperature of the vapour after it has passed throughthe condensing processes and before the protective gas is returned tothe soldering chamber. The condensing processes and the heating processtake place in time periods before and after soldering of the elements.If the protective gas just is returned to the soldering zone without anyheating, the newly soldered printed circuit boards may suffertemperature shocks. To avoid temperature shocks, the protective gas isheated afterwards to a temperature slightly below the condensationtemperature of the solder heating medium. This leads to condensation ofthe vapour in the soldering zone, but with only limited cooling effecton the printed circuit boards. The condensation of the vapour occursrapidly, so in only few seconds all vapour in the soldering zone hasbeen condensed and will fall down to the bottom as drops. Seen from theoutside, it looks as if the vapour is rapidly lowered to a level belowthe printed circuit board. Afterwards can the printed circuit board beremoved from the soldering zone through a door. In this way it isachieved that most of the solder heating medium is removed from thesoldering zone at the time when the door is opened, and only verylimited amounts solder heating medium are lost to the environment.

The condensed heating medium can be returned to the soldering processthrough a flux-depositing trap comprising cooling means for further fluxcondensation and flux solidification. This provides a very efficientremoval of flux contained in the liquid solder heating medium,especially if the temperature is caused to fall gradually during a flowpath for the liquid. By placing a large number of steps that the liquidhas to pass, solidified flux will be collected on the steps and mayadhere to the surfaces as solidified particles which can manually beremoved later. The end result is a liquid solder heating medium fromwhich all flux particles have been removed. This solder heating mediumis subsequently returned to the boiling equipment placed under thesoldering chamber in which the solder heating medium is reheated.

In the following, the invention is explained with reference to thedrawing, where:

FIG. 1 shows a schematic drawing of a possible embodiment of a solderingapparatus according to the invention,

FIG. 2 shows the same as FIG. 1, but with an open gate,

FIG. 3 shows an embodiment of a soldering zone,

FIG. 4 shows an embodiment of a shutting device as seen from a firstside,

FIG. 5 shows the same as FIG. 4 but from another side,

FIG. 6 shows the same embodiment as FIGS. 4 and 5, but seen from above,

FIG. 7 shows a cut through a possible embodiment of a shutting device,

FIG. 8 shows the same embodiment as FIG. 7, but with the valve mechanismclosed,

FIG. 9 shows a cross-section of a soldering zone comprising a deviceaccording to the invention,

FIG. 10 shows a partly opened top view of a soldering zone comprising adevice according to the invention, and

FIG. 11 schematically shows a flux trap.

The soldering apparatus 2 includes a preheating zone 4, a soldering zone6 and a cooling zone 8. A first conveyor 10 is provided before thepreheating zone 4, whereas the preheating zone contains a secondconveyor 12, the soldering zone 6 contains a third conveyor 14 and thecooling zone 8 contains a fourth conveyor 16. At the entrance of thepreheating zone 4 is disposed a gate 18, between preheating zone 4 andsoldering zone 6 a gate 20, between soldering zone 6 and cooling zone 8a gate 22, and between cooling zone 8 and the surroundings a gate 24. Avessel 26 containing the condensing gas in liquid state is shown belowmeans 28 for shutting off the vessel 26, where the soldering zone abovecontains a protective gas 30. In the preheating zone 4 is shown asoldering item in the shape of a printed circuit board 32 lying on aconveyor 12, and a number of position sensors 60-74 are used fordetermining the position of the items and for opening and closing thegates 18-24.

When starting, an item to be soldered 32 may be placed on a conveyor 10,either manually or automatically, after which a position sensor 62 opensthe gate 18, after which the soldering item 32 moves into the preheatingzone, where gradual heating occurs, so that jumps in temperature areavoided, until a temperature which is lower than the solderingtemperature to which the printed circuit boards are later exposed. Thepreheating may be effected with infrared light or by supplying hot air.The conveyor 12 performs a gradual, advancing movement of the solderingitem 32 until the item 32 comes into contact with a position sensor 66.If the soldering zone 6 is ready for receiving the next soldering item,the gate 20 is opened, and the item 32 is moved into the soldering zone6, after which the gate 20 is closed. In the first place, preparationfor performing the soldering process will take place by flushing of theatmosphere, as additional amounts of protective gas 30 are supplied tothe soldering zone, possibly controlled by a sensor, so that theflushing process is continued until the oxygen concentration is below apredetermined value. When the desired oxygen concentration is attained,the shutting means 28 are opened, and vapours formed in the vessel 26rise up and heat the item 32 to be soldered. The item 32 has atemperature which is substantially lower than the vapours, whereby abeginning condensing of the vapours passing up around the item 32occurs. Energy is deposited by the condensation, thus inducing a gradualheating up of the item 32, possibly at the same time as the conveyor 14moves the soldering item forward through the soldering zone 6. At apoint of time, the soldering temperature is reached on the items 32, andthe soldering process is initiated. This process occurs in the course ofrelatively few seconds, but the temperature is maintained over apredetermined period of time in order to ensure complete soldering onrelatively heavy components. When the soldering process is finished,protective gas 30 is blown into the soldering zone, where thisprotective gas has a temperature that imply forced condensation of thecondensing vapours, and simultaneously therewith the shutting means 28are closed so that further vapours are not supplied to the solderingzone. When the vapours are shut down, the gates 22 are opened, and theconveyor 14 provides for transporting the items 32 into the coolingzone. A conveyor 16 takes over here for further transport of the item 32to be soldered while a controlled cooling takes place. A position sensor68 provides for closing the gate 22, and when the conveyor 16 hasadvanced the item 32 to a position sensor 70, a gate 24 is opened. Thisremains open until the item has passed which is detected by sensor 72.

FIG. 3 shows a detail of a possible embodiment of soldering zone 6. Thesoldering zone 6 contains a conveyor 14 which runs between a gate 20 anda gate 22. A vessel 26 containing condensable vapours in liquid phase iscovered by a shutting device 28, where the soldering zone contains aprotective gas 30 blown in through a pipe 34, where an exhaustion 36removes excess protective gas from the soldering zone 6. The solderingvessel 26 is heated by heating elements 40 that e.g. may electricallyheated.

The vessel 26 and heating elements 40 are surrounded by insulationmaterial 42, and the upper part of the soldering zone is surrounded byinsulation material 44. Perforated plates 50 and 52 lie over the vessel26, where the perforated plates can be moved mutually by at least oneactuator 54, whereby the shutting device 28 is formed. By using theoptimal perforation pattern, up to 50% of the total area may be openedfor through-flow of gas or vapours, whereas a very little movement ofthe plates 50, 52 by the actuator 54 may cause complete closing of theopenings formed by the perforations.

In a soldering process, heating elements 40 are switched off and theshutting device 28 is closed simultaneously with protective gas issupplied through the pipes 34, where a item to be soldered, possiblyplaced on conveyor belt 14, is in principle flushed with protective gasuntil the oxygen concentration in the soldering section is sufficientlylow, after which the inflow of protective gas is reduced and shuttingdevice 28 is opened at the same time as more power is supplied to theheating elements 40. A strong vapour formation will hereby occur upthrough the soldering zone 6, and condensation of vapours will occurupon the item to be soldered, thereby heating the item until it reachesthe desired soldering temperature. Before opening the gates again, onemay advantageously supply protective gas in large amounts for completelyremoving the condensing vapours from the soldering zone bysimultaneously closing the shutting device 28 and reducing the powersupply in the heating elements 40, one may achieve that the condensingvapours are entirely removed at the time where gate 22 is opened. Theprotective gas might be recirculated through condensation means forvapour condensation and flux filtration.

FIG. 4 shows a possible embodiment of a shutting device 28 as seen froma first side. The device for shutting off 28 consists of two plates 50,52 that have a number of conical holes 56, which are superposed oppositeto each other in pairs so that through-going apertures are achieved. Thelowermost plate includes a projection 58 that interacts with a recess59. The plates 50, 52 may be displaced mutually, projections 58 andrecess 59 ensuring a relative linear movement in one direction.

FIG. 5 shows the same embodiment as FIG. 4, but seen from the otherside, where the same reference numbers are used. It appears from FIG. 5,that the upper plate 52 may be displaced to the left whereby theapertures 56 are closed.

FIG. 6 shows the same embodiment as FIGS. 4 and 5, but seen from above.From this appears that the plate 52 may be moved to the left in relationto the plate 50 whereby the holes 56 are shut off.

FIG. 7 shows a cut through a possible embodiment of a shutting device100, which comprises three plates 102, 104, 106. Each of the plates 102,104, 106 comprises holes 108, 110, 112. These three holes form athrough-going opening between a volume over the plates and the volumeunder the plates.

FIG. 8 shows the same embodiment as FIG. 7, but with the valve mechanismclosed. It is from FIG. 8 seen that the plate 104 is moved withreference to the plates 102 and 106. In this manner a misalignmentbetween the openings 108, 110, and 112 is achieved. hereby the shuttingdevice 100 is closed.

It is possible to build the shutting device 100 with the plates 102 and106 as fixed plates, where only the plate 104 is movable, which meansthat plate 104 could be in mechanical connection to an actuator devicenot shown. Depending on the shape of the holes 108, 110, and 112 only alimited movement of the plate 104 is necessary for opening a relativelylarge area through the shutting device 100. The shape of the holes 108,110, 112 can have any possible form, and perhaps even specially designedholes would perform a good closing mechanism with a minimal movement ofthe plate 104. Circular holes are a possible solution, but othergeometrical shapes of holes 108, 110, and 112 might by better.

FIG. 9 shows a cross-section of a soldering zone 202 having a tray (notshown) below the soldering zone and comprising heating elements forevaporation of medium 204 that evaporates and forms a vapour 206 thatpartly fills the soldering zone. The soldering zone comprises a conveyorbelt 208 on which a device 210, e.g. a printed circuit board, is seen.The soldering zone is limited by the doors 212 and 214 which are shownas being closed, and at the bottom of the soldering zone, a steam valve216 is shown which valve 216 in an open state forms a large number ofsmall holes which open passage of vapour generated from the boilingliquid below. Above the steam valve 216, a screen 218 has been placed,primarily for collecting components falling off from printed circuitboards 210 during the soldering process. In order not to contaminate ordestroy the valve 216, a closed circuit 220 for purifying the vapour 206is provided. The closed circuit 220 comprises an inlet 222 connectedwith at least one tube 224 leading to a flange 226 from which the vapour206 and flux or other gasses 260 enters a chamber 228 where a firstcondensing unit 230 is placed. Below the unit 230 a filter screen 232 isplaced for collecting liquefied or solidified particles. Further in theflow direction of the vapour 206 and flux or other gasses 260 a secondcondensing unit 234 is placed. Below this condensing unit 234 a filterscreen 236 is placed for collecting liquid or solidified particles.Further in the flow direction of the vapour 206 or gases, a heatingelement 238 is placed, which element is formed in the same way as thecondensing units. Below the heating element 238 a filter screen 240 isplaced for collecting liquid particles. After passing the heatingelement 238, gases enter a chamber 242 from which a tube 244 leads to ablowing unit 246 which blowing unit returns gases 260 to the solderingzone via an inlet 248. The condensing units 230 and 234 can be made asheat exchangers 250 and 252. The heating element 238 can also be made asa heat exchanger 254. The vapour 206 can be mixed with a protective gas260 which passes through the whole unit 220 mixed up with the content ofvapour, flux and other gasses. The heat exchanger 250 and 252 maycomprise cooling fins 262 and 264 tilted against the flow direction. Theheat exchanger 252 also contains fins 266 tilted against the flowdirection. The surfaces in contact with the solder heating media can becoated with a material which having ability not to fix liquid orsolidified flux.

In operation, a printed circuit board 210 is heated by evaporated solderheating medium 204 forming a vapour 206. During the soldering process,the blowing means 246 are not in operation. Thus vapour 206 rises fromthe underlying tray where a heating element is in operation forproducing the vapour 206. At the beginning, the vapour 206 will condensewhen contacting the printed circuit board 210, but this condensationleads to a temperature rise on all the surfaces of the printed circuitboards 210 up to a temperature at which the soldering process takesplace. When the soldering process is completed, which takes only a fewseconds after reaching the correct temperature, a blower unit 246 isstarted, and protective gases 260 are led into the chamber. The gaseshave a temperature below the condensation temperature of the vapour 206.This leads to rapid condensation of vapour 206 which drops down on thesteam valve 216 through which it passes as a liquid to the tray below. Alarge part of the vapour 206 is discharged through the outlet 222 andthe tube 224, and led into the chamber 228 where the vapour passesthrough the condensing units 230 and 234. The content of evaporated fluxand vapour 206 is totally condensed when it has passed these twocondensation units 230 and 234, but the protective gas 260 continuesthrough the heating element 254 and is preheated before it is once againsent through the blowing unit 246. Not until the major portion of thevapour 206 has been removed from the soldering chamber, are the printedcircuit boards 210 removed through a door 212 that can be opened.Afterwards another door 214 can be opened and the next printed circuitboard 210 can be led into the soldering zone. In practice, depending onthe sizes of the printed circuit boards 210, several boards 210 can besoldered simultaneously in the soldering zone.

FIG. 10 shows the closed circuit 220 seen from above. Inlet tubes 224are shown at the top of the figure together with inlet flanges 226leading to the inlet chamber 228 containing a mixture of vapour 206 andprotective gas 260. Afterwards this mixture of gasses passes through thecondensing unit 230. Below the condensing unit 230 a filter screen 232is placed. Further in the flow direction of the gas, a second condensingunit 234 is placed below which a filter screen 236 is placed. The gas isled through the heating element 238 below which a filter screen 240 isplaced. The protective gas 260 enters the chamber 242 from whichconduits 244 lead to blowing units 246.

FIG. 11 shows a closed circuit 320 containing a vapour 306 and aprotective gas 360. At the bottom a collector tray 356 is placed fromwhich an outlet 358 leads to a flux trap 322 comprising steps 324 wherevapour 306 after condensation forms solder heating liquid 104 whichflows over the steps 324 of the trap to an outlet 328 where the entiretrap is cooled by cooling means 326, where the now cooled and purifiedsolder heating medium 304 via an outlet 330 is returned to the solderingzone. In the flux trap 322 liquid fluxes is heavier than the liquidsolder heating media, and the flux is mostly flowing under the liquidsolder heating media 304, where the flux is in contact with the steps324. Flowing down the steps the temperature of the steps 324 isdecreased downwards, and the flux is solidified during the passage ofthe steps 324, but solidified flux is forming glue which is retracted tosteps 324. A cleaning of the steps 324 is necessary as part of normalmaintains of the soldering machine.

1. A soldering apparatus, preferably for soldering items that have beenapplied a soldering agent, where the soldering apparatus includes atleast one soldering zone, where the soldering zone includes means forgenerating vapour, the apparatus being adapted to heat the items to besoldered to a temperature required for soldering by condensing thevapour, and where the soldering zone includes gates, where the solderingzone contains a protective gas, wherein the soldering zone includesmeans for shutting off the vapour generating means wherein the solderingzone His adapted for supplying means for forced condensing of condensingvapour at the end of a soldering process.
 2. A soldering apparatusaccording to claim 1, wherein the apparatus is arranged to supplyprotective gas through ducts to the soldering zone at the start of asoldering process, the supplying of protective gas being effected independence of a measurement of the actual oxygen content in thesoldering zone.
 3. A soldering apparatus according to claim 1, whereinthe apparatus is provided with suction facilities for removingcondensing vapour and protective gas corresponding to the suppliedamount of protective gas from the soldering zone, wherein the apparatusis adapted for supplying protective gas at a regulated temperature lowerthan the soldering temperature in the soldering zone for achievingforced condensing of the condensing vapour, wherein the apparatus isadapted to supply protective gas to the soldering zone at a first hightemperature at the end of a soldering process, where the temperature isapproached a second lower temperature over a period of time.
 4. Asoldering apparatus according to claim 3, wherein the apparatus isadapted for forced condensation by use of recirculation throughcondensing means and through means for flux filtration.
 5. A solderingapparatus according to claim 4, wherein the soldering zone includes avessel to be heated by at least one heating element, wherein the vesselis covered by the means for shutting off, including at least one fixedperforated plate that may interact with at least one displaceableperforated plate which may be displaced by at least one actuator.
 6. Asoldering apparatus according to claim 5, wherein the apparatus isadapted to have the means for shutting off the vessel closed until thestart of a soldering process, wherein at least one heating element maybe activated at the start of the soldering process simultaneously withopening the means for shutting off the vessels, where the apparatus isadapted for closing the means for shutting off the vessel simultaneouslywith regulating the means for heating by ending a soldering process. 7.A soldering apparatus according to claim 6, wherein the apparatusincludes a preheating zone for preheating items to be soldered to apredetermined temperature, wherein the soldering apparatus includes atleast one gate between the preheating zone and the soldering zone,wherein the preheating zone includes at least one gate at its entrancewhere the preheating zone is supplied with protective gas, whereinsuction facilities from the preheating zone reduces the oxygen contentin the preheating zone.
 8. A soldering apparatus according to claim 7,wherein the apparatus includes at least one cooling zone, wherein theapparatus includes at least one gate between the soldering zone (6) andthe cooling zone, and that the cooling zone includes at least one gateat the exit.
 9. A soldering apparatus according to claim 8, wherein thesoldering apparatus includes means for determining the position of theitems to be soldered, wherein the opening and closing functions of thegates of the apparatus can be determined from the position of the itemsand the actual conditions in the zones of the apparatus.
 10. Anapparatus wherein the apparatus comprises means for condensation of avapour containing flux, wherein pumping means circulate the vapourcontaining flux through the condensation means, wherein the condensationmeans comprise a heat exchanger for cooling the vapour for flux andvapour condensation, wherein said pumping means are stopped during thesoldering process, and started upon ending a solder process, wherein thepumping means operate in a closed circuit starting at an outlet from thesoldering process and ending at an inlet to the soldering process,wherein the closed circuit comprises at least a first heat exchangeroperating at a first temperature, and at least a second heat exchangeroperated at a second lower temperature, wherein the heat exchangers areplaced in conjunction with liquid collecting means.
 11. An apparatusaccording to claim 10, wherein the closed circuit also comprises atleast one heat exchanger for heating protective gas to a temperaturebelow the condensing temperature of the vapour before the protective gasis returned to the soldering device in a time period after soldering isfinished.
 12. An apparatus according to claims 11, wherein liquefiedsolder heating medium is returned from the liquid collecting meansthrough a conduit to a flux trap comprising steps, which flux trap iscooled by cooling means, first to a temperature for condensation andsubsequently further cooled to a temperature for flux liquefying.
 13. Anapparatus according to claims 12, wherein the heat exchangers comprisecooling fins that are tilted against the inlet direction in order toreturn liquefied solder heating medium and liquefied or solidified flux,wherein protective gas passes over and around the fins.
 14. An apparatusaccording to claim 13, wherein liquefied solder heating medium andliquefied or solidified flux passes filter means before reachingcollecting means, which filter means collect liquid or solidified fluxand other unwanted chemical substances.
 15. An apparatus according toclaims 14, wherein liquid solder heating medium is collected at thesurface of a tray placed under the soldering zone and led over the fluxtrap.
 16. An apparatus according to claim 15, wherein surfaces onelements in contact with flux are coated with a material having abilitynot to fix liquid or solidified flux.
 17. An apparatus according toclaim 16, wherein the pressure in the soldering zone is reduced at thebeginning of a soldering process, wherein the pressure is partlynormalised by opening a valve for supply of protective gas into thesoldering zone, wherein the pressure in the soldering zone is normalizedby opening for supply of vapour.
 18. A method for soldering in whichitems to be soldered are applied a soldering agent in advance, whereinthe items are preheated in a first step, wherein the items are solderedin a second step in that condensing vapour heats the items to atemperature, which is higher than the melting point of the solderingagent, wherein the soldering items are cooled in a third step subsequentto soldering, wherein the second step is effected in the presence of aprotective gas, wherein the second step includes shutting off the supplyof vapour and forced condensing of vapour.
 19. A method according toclaim 18, wherein the supplying of protective gas is used as means forforced condensing of vapour.
 20. A method according to claim 19, whereinthe method comprises flux deposition in conjunction with vapour phasesoldering, which soldering process leads to evaporation of flux andother chemical substances, wherein the vapour of solder heating mediumcontaining flux and other chemical substances is drawn into a closedcircuit in time periods between or after soldering processes, whereinthe closed circuit comprises at least a first condensation process and asecond condensation process, which first and second condensationprocesses take place at a first high temperature and at a second lowertemperature, and wherein liquid solder heating medium is returned to thevapour phase soldering process.
 21. A method according to claim 20,wherein the first temperature depends on the condensation temperature ofthe flux, wherein the second temperature depends on the condensationtemperature of the solder heating medium.
 22. A method according toclaim 21, wherein the protective gas is heated by heating means to atemperature below the condensation temperature of the vapour after ithas passed through the condensing processes and before the protectivegas is returned to the soldering chamber, which condensing processes andthe heating process take place in time periods after soldering of theelements.
 23. A method according to claim 22, wherein the condensedheating medium is returned to the process, wherein it is led through aflux depositing trap, which trap comprises a cooling process for fluxcondensation and flux solidification.